Analyte protectants

Discussions about GC and other "gas phase" separation techniques.

3 posts Page 1 of 1
Hello,

Our lab performs environmental & food analysis, and I'm in charge of developing new / optimizing current procedures / troubleshooting.

We are having some troubles with the GC-MS/MS analysis of organophosphorous pesticide residues. Basically the signal for most compounds enhances strongly in samples compared to calibration standards: the so-called matrix enhancement effect. This leads to recoveries of internal standards up to 600%.

Because the quantification is relative, internal standards compensate for this effect. But we use ~6 internal standards for ~20 analytes, and the effect is different for different types of samples. Therefore i found it impossible to quantify each batch of samples without juggling internal standards around to find the best combinations for that particular run.

I've been doing some literature research and people recommend the use of analyte protectants. I think i have a good idea on what/how much to inject with each sample but I was wondering if people here have experience with using these? And more specifically if i should be worried about the long-term effects on the system?

An external expert told me that some labs 'just add a drop of olive oil to every vial'. But I want to do this more controlled/reproducible and with minimal risk of damage to the system. What's the best way to start this safely? The injection is 25µl of hexane in PTV solvent vent mode. Is the best way to add the protectants to the vials, or let the autosampler fill the syringe with 25µl sample and then 1µl of the protectant solution?

Thanks in advance!
I've been playing with them; they really do help to eliminate the matrix effects you see with certain foods/analytes. I've just used the general mixture that Maskovska, Anastassiades et al published and that EURL picked up:

http://www.eurl-pesticides.eu/library/d ... on-APs.pdf

I've also tried using the concentrated cucumber extract that Anastassaides et al published. It works pretty well. I know it sounds a lot like "a drop of olive oil" but I've had really good success with it. I think I'd recommend it over the analyte protectants, although the combination works better than either one alone. I made a concentrated cucumber extract (Quechers, no cleanup) by drying down the normal extract 10 fold and then used that to make the analyte protectant mixture. I add 30 uL to each mL of normal extract and shoot.
Mark Krause
Laboratory Director
Krause Analytical
Austin, TX USA
Interesting, thanks for the link (and bringing up my first post in this forum, IIRC 8)).

In the meantime, after experimenting, we've settled on using a mixture of gulonic acid gamma lactone and 3-ethoxy-1,2-propanediol in acetone (500ppm each). We don't add it to the extract, it's placed in a separate vial on the autosampler and programmed to inject 1µL with our 25µL (solvent vent) standards/samples injections on GC-MS/MS. It works nicely for the kind of analyses I described in the OP, and we didn't notice negative long-term effects, but I have to say it's not used for the bulk of the analyses on that instrument.
3 posts Page 1 of 1

Who is online

In total there is 1 user online :: 0 registered, 0 hidden and 1 guest (based on users active over the past 5 minutes)
Most users ever online was 1117 on Mon Jan 31, 2022 2:50 pm

Users browsing this forum: No registered users and 1 guest

Latest Blog Posts from Separation Science

Separation Science offers free learning from the experts covering methods, applications, webinars, eSeminars, videos, tutorials for users of liquid chromatography, gas chromatography, mass spectrometry, sample preparation and related analytical techniques.

Subscribe to our eNewsletter with daily, weekly or monthly updates: Food & Beverage, Environmental, (Bio)Pharmaceutical, Bioclinical, Liquid Chromatography, Gas Chromatography and Mass Spectrometry.

Liquid Chromatography

Gas Chromatography

Mass Spectrometry